1. Field of the Invention
This invention pertains to methods and apparatus for vacuum forming a vehicle wheel from a mixture of urethane constituents.
2. Prior Art
The present invention is in a wheel that is formed from a urethane material in a vacuum forming apparatus in a single casting operation to have at least the strength, or greater, of a like size and load bearing standard steel or aluminum wheel for mounting a tire thereon. The vacuum forming apparatus includes a mold having a cavity wherein is formed a wheel. Or the cavity is formed to accommodate a wheel core fitted therein, that is preferably formed from a light gauge steel or appropriate aluminum compound, and is supported in the mold by spacers to receive a urethane coating. In practice, a urethane material, that is a compound formulated to produce a steel like strength, is pulled under vacuum into a mold cavity. Whereby, after curing, the mold is opened and a homogenous wheel, or a wheel containing a core, is removed.
Relating to vacuum forming apparatus, heretofore it was recognized that venting air from a tire tread mold cavity early in a casting process could eliminate the necessity for venting the cavity through spaced holes in the mold that materials from the tread will flow into during casting and form projections or “tits”. Such extensions or “tits” project from the tread surface and were either pulled off when the tire was removed from the mold, had to be cut off or wore off during tire use. To prevent this undesirable cosmetic anomaly it was recognized that air could be vented from the mold cavity just before tread casting, eliminating a necessity for providing flow passages or vents from the tire tread mold while still obtaining a smooth, un-pocketed or un-blemished, finished tread surface. Examples of such an introduction of a vacuum into a tire mold just prior to forming a tire tread are shown in U.S. Pat. Nos. 4,573,894 and 5,152,951. Specifically, U.S. Pat. No. 4,573,894 sets out a tire mold having a cavity that is for receiving and finally shaping the tire. The patent is defined by a surface that is for contacting the exterior of the tire during tire curing. The cavity is fluid connected to a single vacuum source for evacuating air from within the cavity during an early portion of a tire curing cycle to prevent air and any other fluid from becoming trapped between the tire and the surface that defines the cavity that will become the tire tread. Visual effects in the form of voids in the tire exterior are, thus eliminated. Like the '894 patent, U.S. Pat. No. 5,152,951 also provides for the elimination of fluid from the mold cavity during an early portion of a tire curing cycle. The patent provides for fluid evacuation through a space between the surfaces of the mold parts that defines the mold parting line. Both patents provide a single vacuum source and its connection to the mold cavity for forming the tire side wall and tread surfaces.
Recently, the inventors of the present invention developed an improved vacuum forming apparatus for forming transport tires that is the subject of a currently pending U.S. patent application Ser. No. 10/936,635, filed Sep. 4, 2004. This patent application sets out an apparatus and method for forming an elastomer tire containing plies, belts and beads, that involves both an evacuation of air from the elastomeric mixture prior to its introduction into the mold cavity, and for pulling the air free mixture through the mold. Which air free flow of elastomeric material fills an area between inner and outer mold walls and travels through the core of plies, belts and beads, to form a finished transport tire that is free of voids or pockets. Unlike this earlier patent application the present invention provides for vacuum forming a homogenous wheel or a wheel core having an outer coating of a urethane material bonded thereto.